1. Field of the Invention
This invention relates to a lighting device, in particular, to a lighting device to emit a light which hardly causes stress when used in illumination.
2. Description of the Prior Art
In the case of doing visual tasks, the use of inappropriate illumination is causative of stress. For example, when workers are involved in a long-time video display terminal VDT task or chemical analysis, the resultant hypertonic in their optic nerves causes stresses which may lead in extreme cases to metabolic and/or mental disorder. In particular, VDT task is very causative of stress even when the operation time is not so long, thus the operators come to usually complain of headache, inappetence and/or languor. Because of these, in visual tasks accompanying tensions in the optic nerve, the use of a less stress-causative lighting device is indispensable.
Although with the spread of computers, discussions have been made on illuminations which are feasible in VDT task for less languor, no effective illumination is available which is worthy of special selection. Past discussion on illuminations have been focused on their clarity and color rendering properties and no discussion has been actually made on the relationship between illumination and stress.